1. Field of the Invention
The process of the present invention relates, in general, to a process of producing long glass fibers and, more particularly, to a drawing process in which glass fibers containing cores of metallic or ceramic materials are produced. The metallic or ceramic cores of the glass fiber can be located on or about the axis of the glass fiber.
2. The Prior Art
Glass fibers with metal cores have long been made by variations of the method described in U.S. Pat. No. 1,793,429. Versions of this process, in which long fibers can be made, generally consists of maintaining a small pool of molten metal in the fused tip of a glass tube from which a fiber is drawn. The glass tube is fed at a constant rate into a heated zone, and the molten metal pool is maintained by feeding a wire or rod of the metal into the pool through the open end of the tube. These methods can be used to make fibers having lengths that are limited only by the volume of glass, but these process have several serious shortcomings. Principal among these problems is that the glass-to-metal ratio cannot be accurately controlled because the metal filament diameter depends on the properties of the glass and on several of the processing parameters.
These methods have produced only solid core metallic or ceramic filaments in solid glass fibers. Another type of process employs filling a glass tube with a solid charge of metal or a loose powder. A problem with this approach is that the change in volume of the charge as it melts causes a gap to form between the melt and the unfused charge. This gap causes instability during processing and leads to the production of fibers having nonuniform dimensions.
U.S. Pat. No. 3,640,693 discloses a method for making glass fibers containing a filament of silicon, the method consisting of a two-step process. In the first step, the glass is filled with powdered silicon evacuated and heated to vacuum cast the silicon onto a solid metal core, completely filling the inside diameter of the tube. The resultant silicon-filled tube is then heated without vacuum to the working temperature of the glass, while drawing a fiber therefrom.
It is desirable to have a process in which the tube can be maintained in close contact with the charge at all times in order to maintain uniform temperature gradients along the tube and the charge. Such a process could be used to promote more uniform fiber geometry.